Blood temperature and perfusion to exercising and non-exercising human limbs

Temperature-sensitive mechanisms may contribute to blood-flow regulation, but the influence of temperature on perfusion to exercising and non-exercising human limbs is not established. Blood temperature (T-B), blood flow and oxygen uptake ((V) over dot(O2)) in the legs and arms were measured in 16 healthy humans during 90min of leg and arm exercise and during exhaustive incremental leg or arm exercise. During prolonged exercise, leg blood flow (LBF) was fourfold higher than arm blood flow (ABF) in association with higher T-B and limb (V) over dot(O2). Leg and arm vascular conductance during exercise compared with rest was related closely to T-B (r(2)=0.91; P<0.05), plasma ATP (r(2)=0.94; P<0.05) and limb (V) over dot(O2) (r(2)=0.99; P<0.05). During incremental leg exercise, LBF increased in association with elevations in T-B and limb (V) over dot(O2), whereas ABF, arm T-B and (V) over dot(O2) remained largely unchanged. During incremental arm exercise, both ABF and LBF increased in relationship to similar increases in (V) over dot(O2). In 12 trained males, increases in femoral T-B and LBF during incremental leg exercise were mirrored by similar pulmonary artery T-B and cardiac output dynamics, suggesting that processes in active limbs dominate central temperature and perfusion responses. The present data reveal a close coupling among perfusion, T-B and aerobic metabolism in exercising and non-exercising extremities and a tight association between limb vasodilatation and increases in plasma ATP. These findings suggest that temperature and (V) over dot(O2) contribute to the regulation of limb perfusion through control of intravascular ATP.